How to varnish floorboards

Inspired by a helpful YouTube guide. We based this walk-through on the Ronseal UK video "Ronseal DiamondHard Floor Varnish: How to varnish a wooden floor". It shows the full process from bare boards to finished coats - particularly useful for the between-coat sanding steps that a lot of guides skip past.

1. Check the boards and punch down any nails

Walk the floor and listen for squeaks. Any board that moves needs screwing down - a squeak that annoys you now will annoy you every day through three coats of varnish.

Use a nail punch to sink any protruding nail heads below the surface. A nail head above the surface will tear the sanding disc and leave a long scratch. Take your time here.

2. Fill gaps between boards

Gaps let draughts up and collect dirt. For small gaps, a flexible wood filler works well - choose a colour that matches the wood rather than basic pine filler on an old oak floor. Press it in firmly and scrape the surface flush.

Mind you, very wide gaps are better filled with thin strips of wood glued in place. Filler in a gap wider than about 8 mm will crack over time as the boards expand and contract.

3. Sand the floor in stages

Hire a drum sander for the main area and an edge sander for the perimeter. Start with a coarse grit - 40 or 60 - running at 45 degrees to the boards if they are very rough, then switch to 80 grit along the boards, and finish with 120.

Keep the machine moving. Stopping while it is running will gouge a hollow. Overlap each pass by about a third. When you are done, vacuum thoroughly and wipe with a slightly damp cloth. Dust in the varnish is the enemy.

4. Apply the first coat thinly

Use a wide brush or a floor applicator pad. Work in the direction of the grain, from the far end of the room back towards the door so you do not paint yourself into a corner.

The first coat is a sealing coat. It goes on thin and soaks into the wood. It will look a bit patchy and that is fine. Leave it to dry fully - do not rush this.

5. Lightly sand between every coat

Once the first coat is dry, go over the whole floor with 180 grit sandpaper by hand or with a random orbit sander. You are just knocking back the raised grain and any bits of dust, not taking the coat off.

Vacuum again and wipe down before the next coat. Every coat after this one goes on slightly thicker than the last.

6. Apply two or three more coats

Most floor varnishes need three coats minimum for a durable finish - some manufacturers recommend four in high-traffic areas. Sand lightly and clean between each one.

The final coat gets no sanding afterwards. Apply it evenly, avoid going back over wet varnish, and leave the room alone until it is fully cured. Walking on it too soon is the most common way to ruin an otherwise decent job.

7. Stay off the floor until it has cured

Dry and cured are different things. The floor might feel dry to the touch in a few hours, but full hardness takes much longer - sometimes several days depending on the product and temperature. Check the tin.

Keep the room warm and ventilated. Cold slows curing right down. Open windows help the solvents off-gas without making it too cold to cure.

When to call a handyman

Call Richard if the boards need replacing before the varnishing starts, if the floor has a lot of damage, or if the job is simply more than you want to take on. Floor sanding is hard work and the hire equipment is heavy.